UK Insect Decline and Extinctions
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POSTNOTE Number 619 March 2020 UK Insect Decline and Extinctions Overview ◼ There have been documented declines in insect species and populations. Generalist species are less likely to decline than more specialised species. The impacts of this on ecological processes are poorly quantified. ◼ The UK has unparalleled data from long- term monitoring, but it is limited by gaps in what is measured and how. There are few long-term data sets with abundance data. Insects provide vital goods and services for ◼ Drivers of decline, such as habitat loss, are wildlife, food production and human health, common across insect groups and can and their decline threatens important natural interact to cause combined pressure on processes. Despite some insects being in long- populations. However, environmental term decline, a few species are showing stable changes can benefit some species while or increasing trends. Insects can respond to negatively affecting others. interventions quickly. This POSTnote will ◼ Interventions, such as habitat creation, may summarise the evidence for insect declines in play a role in halting declines, but the scale the UK, the drivers of trends, and interventions and types need careful consideration. to support the recovery of insect populations. Background Limitations of UK Insect Decline Data Insects play a pivotal role in natural processes that support An ideal dataset for understanding insect decline would include other living organisms, and human health and well-being insects from a wide range of ecosystems, using samples (POSTnote 281). Adult insects have six legs and usually one or collected in a standardised way.3,39,40,20,33 Globally, data on two pairs of wings and are the most diverse group of animals.1– 4 Roles include pollination (POSTnote 348 and 442), pest and Box 1: Economic Importance of Beneficial Insects weed regulation, decomposition, nutrient cycling, and provision Insects have economic, social and cultural value.2,9,41–43 A of food for wildlife and humans (Box 1). They can also be decline in insects may negatively impact ecosystem services,44,45 and could be costly.46 Currently, there is limited agricultural pests or transmit disease (Box 2).5–18 Insects are evidence for the quantitative value of ecosystem services 9,19,20 key indicators for monitoring ecosystems (POSTnote 312). provided by insects, but some examples are emerging. The economic value of pollination to UK crop production is Concerns about insect decline attracted wider attention approximately £500 million a year.47,48 Dung beetles are following studies showing large declines in insect abundance estimated to be saving the UK cattle industry £367 million and biomass.21–23 Recent media attention has claimed each year and £37.42 per cow through reducing flies and 49 unprecedented declines in insects across the globe leading to increasing nutrients in the soil. Natural pest control (by ground beetles and parasitoid wasps) of widespread aphid an ‘insectageddon’24 causing the “collapse of nature”.25 These pests is worth up to £2.3 million per year in South East claims were largely based on a review of scientific articles from England wheat fields alone.46,50 Freshwater insects in their across the globe.26 However, this study has been criticised as larval stage, such as dragonflies or mayflies, can also filter the evidence it reviewed was predominantly from North water, remove pollutants and provide food for bats17, birds51 52 America and Europe, which may have skewed the conclusions. and fish (such as salmon and trout ). This supports It also excluded studies that reported stable or increasing recreational activities, including angling (which contributed £1.46 billion to the English economy in 201553). Insects also populations by only selecting those showing a decline.27–31 As have social and cultural value.54 Some studies have such, the trends for global insect populations remain largely attempted to quantify the value the public place on insects; unknown but could be underestimated.32,33 However, studies in for example, a study found that people were willing to pay Europe found insect abundance or biomass declined between approximately £43 per household per year to support bee 55 38% and 75%.21,34–38 protection policy; equating to £842 million per year when scaled up to 31 million taxpayers. The Parliamentary Office of Science and Technology, Westminster, London SW1A 0AA 02072192840 [email protected] parliament.uk/post @POST_UK POSTNOTE 619 March 2020 UK Insect Decline and Extinctions Page 2 insects are limited because of the large number of species.1,3,56 mammals, plants and insects (4–8%).19 However, a study found The UK has more data than many countries due to its long-term that butterfly distribution declined more than birds and plants.34 recording schemes, natural history collections, citizen science engagement and insect research community.57,58 Emerging Declines in abundance or distribution have been seen in bees 32,101 34 35 102 labour-efficient methods can help data collection through and hoverflies, butterflies and moths, beetles, and 48,101,103,104 remotely monitoring larger areas, such as bioacoustics59–62 and freshwater insects. However, some species are 105 BioDAR63–65 (see POSTbrief 36).66 New identification methods increasing in biomass. The data available for the most such as DNA analysis may prove more reliable in the future studied insect groups are summarised below. 67–74 (see POSTbrief 36). New methods still require expert Bees and Hoverflies interpretation. Current data are limited by gaps in what is Bees and hoverflies experienced dramatic losses between the measured and how, including:3,40 1950s and 1980s but losses have slowed since the 1990s.77 Of ◼ Methods. Surveys that used a standardised sampling across 353 wild pollinator species, 117 (33%) had decreasing sites, measured at systematic intervals, exist for a limited distributions (1980–2013).32 Yet, 10% of species had increasing group of species and habitats.40,75–78 distributions.3297 The rest (57%) had an unclear trend.32 ◼ Time. Limited data are available before the 1970s,79 creating Pollinators key to European crops increased by 12%, potentially an arbitrary baseline for comparison.40,80 Using data collected supported by agri-environment schemes or the increased area irregularly across time may lead to uncertainty.56,81,82,33 of oilseed rape.32,106,107 Since 1909, 20 bee and wasp species ◼ Location. The gaps in where data are collected can lead to have gone extinct in Britain.108 a bias towards some habitats such as nature reserves and agricultural systems. The trends from these systems may not Butterflies and Moths be transferable to other systems. This bias has begun to be Of 62 butterfly species, 19 (31%) are threatened and four have 40,76,81,82 addressed through several schemes. gone extinct in GB.109 Butterfly abundance has declined for 21 ◼ What is measured. Data focus on specific insect groups; species since 1976.110 However, abundance increased for 11 such as bees,83 rather than other groups, such as species111 (such as silver-washed fritillary with a 127% decomposers;2,3,56,84 and more easily observed adult forms increase).112 Of 337 moth species, 111 (33%) had increasing rather than caterpillars or aquatic larvae.66 trends but 222 (66%) were declining, and 71 species declined ◼ The type of data can affect the conclusions made about by over 30% per decade (1968–2004).100 Total GB moth insect declines. For example, species richness tells us the abundance has decreased by 31% (1969-2016).100,113Moth number of species present. However, abundance (number of declines occurred in coastal, urban and woodland habiats.113 individuals of a species) may have a stronger link with However, some evidence suggests that moth biomass may be ecosystem services than richness.9,21,45,85–87 Without knowing increasing, implying that a few species are doing well.79 the abundance and species identity, changes in communities can be masked.88 The range of data can make comparisons Beetles 98 across insect groups, locations and time difficult but Of 1134 beetle species in GB, 13% are threatened. A statistical modelling can be used.85,89 significant decline in abundance of ground beetles was found in ◼ Who is collecting data. The reliance on volunteers means 75% of 68 species, and 34 of those species decreased by 30% 102 that there is often irregular sampling.39,85,90 To continue each decade (1994–2008). The number of species also collecting data, long-term investment into resources, building declined.102 However, abundance in chalk downlands, skills and capacity, is required to sustain volunteers, support woodlands and hedgerows increased (16–57%).102 amateurs and incentivise professional development.40,91–97 ◼ Accessing data. Some data are fragmented (held privately Box 2: Pests and Invasive Non-Native Species by researchers, or companies like agricultural or While other insects are in decline, there are concerns that 101 environmental consultancies, see POSTbrief 36).40 pest species (native and invasive) such as weevils, aphids,112 and cabbage stem flea beetles110 may be Trends in UK Insects increasing (POSTnotes 303, 394, 439), with negative impacts on crop yields.114,115 Climate change and emerging resistance The UK has experienced extinctions and declines in abundance, of pests to insecticides116 amplifies this increase117 biomass and distribution of insects. Of the 2430 GB insect (POSTnote 597). Although some invasive species can create species assessed by Natural England, 55 have gone extinct and opportunities (such as increased pollen availability), others 286 (11%) are threatened.98 Total aerial insect biomass pose risks (such as increased predation, see POSTbrief 118 declined at one of four sites since 1973.99 Data from 3089 36). The impact of the invasive species depends on the abundance and the role it plays in the system.